How to fill holes in Mesh from Curve from SVG
You will have to fix the topology of this. This is quite a mess. 

A good clean mesh based of quads is easier to fill. To close holes you can select the edges around the hole and press F



I have created this very basic key, by extruding faces from a plane using E with edges selected in top view. You can use the SVG as reference if you want it to match the lines of the model. I then selected all faces in face select mode by double tabbing A and extruded the model up along the Z axis by pressing E.

Then I selected the edges around the model and bevelled them using CTRL+B